Internal combustion engines are known that include a plurality of cylinders that receive a charge flow for combustion in an air-fuel mixture. Modern engine design and controls can result in cylinder-to-cylinder variation in cylinder breathing, pumping work and other conditions that lead to cylinder torque imbalance and undesired noise, vibration and/or harshness. For example, some engines include a dedicated exhaust gas recirculation (EGR) system that creates an imbalance in cylinder breathing conditions. Engines may also use cylinder deactivation or other techniques that cause cylinder-cylinder variation which create torque imbalances.
Existing techniques for addressing torque imbalance include those that use a speed signal for feedback control of the engine torque. However, these techniques suffer from the poor signal to noise ratio from the speed signal. Therefore, further improvements in this technology area are needed.